JUST DESSERTS: Five Examples in Five Minutes


fan.pngHidetoshi and Rothman, 2008,Sacred Mathematics: Japanese Temple Geometry, pg 257

In a sector AOB of radius r, draw a small circle of radius x with center O. Draw the tangent to the small circle from the vertex B. As x is varied, the area S(x) of the black part of the figure will also vary. Show that S(x) is a maximum when x ≅ (293/744)r.


How is the area of the shaded region related to the radius of the circle?
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Derivation of algebraic relationship:



A W-I-N modification of the problem above. How is the perimeter of the shaded region related to the radius of the circle?

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Derivation of algebraic relationship:




rhombus.png Hidetoshi and Rothman, 2008,Sacred Mathematics: Japanese Temple Geometry, pg 118


Find x in terms of a when the area of the rhombus minus the area of the square is maximized


How is the area of the shaded region related to the length of the diagonal?


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Derivation of algebraic relationship:




problem_47.png Hidetoshi and Rothman, 2008,Sacred Mathematics: Japanese Temple Geometry, pg 120


Maximize y as a function of x assuming
BC = a is constant.


How is the area of the square related to the length of the vertical (blue) leg?

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problem_37.png Hidetoshi and Rothman, 2008,Sacred Mathematics: Japanese Temple Geometry, pg 114


Given a rectangle ABCD with AB > BC, circle is inscribed such that it touches three sides of the rectangle, AB, AD, and DC. The diagonal BD intersects the circle at two points P and Q. Find PQ in terms of AB and BC.


How is the length of the (red) chord related to the vertical (blue) side of the rectangle?

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Derivation of algebraic relationship:



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